1. Field of the Invention
The present invention relates to an electronic device such as a cellular mobile phone and, more particularly, to an electronic device having a shield structure with respect to a high frequency component part.
2. Description of Related Art
Conventionally, a cellular mobile phone has incorporated therein a board assembly 90 shown in FIG. 15. In the board assembly 90, a plurality of IC chips 94, 95 constituting a high frequency circuit are mounted on a main board 9. These IC chips 94, 95 are covered with a shield case 91 mounted on the main board 9.
The shield case 91 is constituted of a metallic frame 93 securely soldered onto the main board 9 and a metallic cover 92 fitted into the metallic frame 93.
In order to pack a plurality of component parts incorporated in a cellular mobile phone in a high density, an auxiliary board 96 having a plurality of component parts 97, 98 mounted thereon is securely stuck onto the shield case 91 via a double-faced adhesive tape or the like.
In the above cellular mobile phone, the component parts 97, 98 mounted on the auxiliary board 96 may be required to be positioned with high accuracy.
In this case, it is conceived that a positioning piece (not shown) projects from the metallic cover 92 constituting the shield case 91, and then, an end face of the auxiliary board 96 abuts against the positioning piece, thus securing the positioning accuracy of the component parts 97, 98 mounted on the auxiliary board 96.
However, in the structure in which the positioning piece of the metallic cover 92 constituting the shield case 91 secures the positioning accuracy of the component parts 97, 98, fitting tolerances and shape tolerances of the metallic cover 92 with respect to the metallic frame 93 are superimposed on the positional deviation tolerances and shape tolerances of the metallic frame 93 securely soldered onto the main board 9, thereby adversely influencing the positioning accuracy of the auxiliary board 96 on the main board 9. As a consequence, there arises a problem that the superimposition of the tolerances obstructs securing of the high positioning accuracy of the component parts 97, 98 on the auxiliary board 96.
In view of the above problem, an object of the present invention is to enhance the positioning accuracy of an auxiliary board on a main board more than that in the conventional art in an electronic device provided with the auxiliary board on the main board via a shield case.